This invention generally relates to an automatic transmission. More particularly, the present invention pertains to a shift control apparatus and method for controlling an automatic transmission to shift a gear stage based on at least two shift patterns, one involving shifting the gear stage based on vehicle speed and throttle opening and the other involving shifting the gear stage based on vehicle speed and road condition.
A known shift control apparatus for an automatic transmission is disclosed in Japanese Patent Laid-Open Publication No. Hei 07-127720. This published application discloses that the shift control apparatus switches between a first shift pattern involving shifting gears based on vehicle speed and throttle opening and a second shift pattern involving shifting gears based on road grade and vehicle speed according to the throttle opening, the range of the shift lever, the gear stage, and the vehicle speed. The shift control apparatus controls the automatic transmission to shift the gear stage based on the second shift pattern when the apparatus judges that the vehicle condition is in a deceleration area. For example, the shift control device judges that the vehicle condition is in the deceleration area when the shift lever is in the D (drive) range, the gear stage is larger than the 2nd gear stage, the throttle opening is less than a predetermined value, and the vehicle speed is larger than a predetermined value.
However, with the shift control apparatus described in the above-mentioned published application, when the apparatus judges for example that vehicle is in the deceleration area after the apparatus has shifted from the 3rd gear stage to the 4th gear stage based on the first shift pattern, the automatic transmission is shifted to the 3rd gear stage again based on the second shift pattern in accordance with the vehicle speed and road grade conditions. That is, the vehicle is shifted down to the 3rd gear stage quickly after the vehicle is shifted up from 3rd gear stage to 4th gear stage in a short time period. The shifting to the same gear stage (3rd gear stage) is thus repeated in a short time period. Therefore, the automatic transmission hunts through repeated shifting, and this causes a problem with respect to a deterioration in the shift feeling.
A need thus exists for a shift control apparatus and method for improving the shift feeling when the shift control apparatus switches between at least two shift patterns.
One aspect of the present invention involves a control apparatus for effecting shift control of an automatic transmission for shifting a gear stage of the automatic transmission based on one of a first shift pattern in which gear stage shifting is based on vehicle speed and throttle opening and a second shift pattern in which gear stage shifting is based on the vehicle speed and a road condition, and with the gear stage shifting being based on the second shift pattern when the vehicle driving condition is in a deceleration condition. A shift control apparatus controls the automatic transmission to shift the gear stage based on the second shift pattern without shifting from a first gear stage to a second gear stage which is higher-speed gear stage than the first gear stage when the vehicle driving condition changes from a condition crossing a shift line which commands a shift from the first gear stage to the second gear stage on the first shift pattern to a condition switching from the first shift pattern to the second shift pattern according to a prescribed condition.
The gear stage is shifted based on the second shift pattern without shifting from the first gear stage to the second gear stage when the vehicle driving condition changes from the condition crossing the shift line on the first shift pattern to the condition switching from the first shift pattern to the second shift pattern according to the prescribed condition. For example, when the vehicle driving condition is changed from the first shift pattern to the second shift pattern by an operation of the driver, even if the vehicle driving condition crosses over the shift line changing from the first gear stage to the second gear stage, the gear stage of the automatic transmission is shifted based on the second shift pattern without being shifted to the second gear stage. The gear stage of the automatic transmission is thus not shifted to the high-speed gear stage (the second gear stage) repeatedly. It is thus possible to decrease extra and repeated shifting. Hunting of the automatic transmission is thus decreased and the shift feeling is improved.
In the present invention, the prescribed condition is the vehicle deceleration condition. More specifically, the prescribed condition is the condition in which the time from the condition crossing the shift line which commands the shift from the first gear stage to the second gear stage on the first shift pattern until the condition switching from the first shift pattern to the second shift pattern is shorter than a predetermined time. The prescribed condition can also be the condition in which the rate of the throttle opening when the vehicle driving condition changes from the condition crossing the shift line which commands the shift from the first gear stage to the second gear stage on the first shift pattern to the condition switching from the first shift pattern to the second shift pattern is larger than a predetermined rate. The control apparatus is thus better able to control the automatic transmission according to the driver""s intention.
According to another aspect of the present invention, a shift control method for an automatic transmission is designed to shift a gear stage of the automatic transmission according to one of a first shift pattern in which gear stage shifting is based on vehicle speed and a throttle opening and a second shift pattern in which gear stage shifting is based on the vehicle speed and a road condition, with the gear stage shifting being based on the second shift pattern when the vehicle driving condition is in a deceleration condition. The method involves judging on the basis of the vehicle driving condition whether to perform gear stage shifting according to the first shift pattern or the second shift pattern, controlling the automatic transmission to shift the gear stage according to the first shift pattern when it is judged on the basis of the vehicle driving condition that gear stage shifting is to be performed according to the first shift pattern, and judging whether the vehicle driving condition changes from a condition crossing a shift line which commands a shift from the first gear stage to the second gear stage on the first shift pattern to a condition switching from the first shift pattern to the second shift pattern. The automatic transmission is then controlled to shift the gear stage based on the second shift pattern without shifting from the first gear stage to the second gear stage when the vehicle driving condition changes to a condition in which gear stage shifting is performed according to the second shift pattern within a predetermined time after the vehicle driving condition crossed over the shift line.
Another aspect of the present invention relates to a shift control method for an automatic transmission that is designed to shift a gear stage of the automatic transmission according to one of a first shift pattern in which gear stage shifting is based on vehicle speed and a throttle opening and a second shift pattern in which gear stage shifting is based on the vehicle speed and a road condition, with the gear stage shifting being based on the second shift pattern when the vehicle driving condition is in a deceleration condition. The method includes judging on the basis of the vehicle driving condition whether to perform gear stage shifting according to the first shift pattern or the second shift pattern, controlling the automatic transmission to shift the gear stage according to the first shift pattern when it is judged on the basis of the vehicle driving condition that gear stage shifting is to be performed according to the first shift pattern, and judging whether the vehicle driving condition changes from a condition crossing a shift line which commands a shift from the first gear stage to the second gear stage on the first shift pattern to a condition switching from the first shift pattern to the second shift pattern. The automatic transmission is then controlled to shift the gear stage based on the second shift pattern without shifting from the first gear stage to the second gear stage when a rate of the throttle opening is larger than a predetermined rate at a time when the vehicle driving condition changes to a condition in which gear stage shifting is performed according the second shift pattern within a predetermined time after the vehicle driving condition crossed over the shift line.
The automatic transmission is controlled to shift the gear stage based on the second shift pattern when the throttle opening is less than a predetermined opening. The automatic transmission can thus be more reliably controlled according to the driver""s intention.